1. Field of the Invention
Embodiments of the present invention generally relate to estimating efficiency and controlling the operation of a downhole pump disposed in a wellbore. More particularly, embodiments of the present invention generally relate to accurately determining a transfer point of a pump stroke and controlling the pump and fluid production of the well based on the transfer point.
2. Description of the Related Art
The production of oil with a sucker-rod pump is common practice in the oil and gas industry. Typically, the pumping system is designed with the capacity to remove liquid from the wellbore faster than the reservoir may be able to supply liquid into the wellbore. In a fluid-producing well that is aided by artificial lift in the form of a rod pumping system, a condition may arise where the pump is not completely filled with fluid on each pump stroke. The well is said to be “pumped off,” and the condition is known as “pounding.”
It is desired to know the quantity of fluid entering the pump on each stroke (the pump “fillage”) for a number of purposes including, e.g., to stop the pumping system periodically to allow more fluid to enter the wellbore or to control the speed of the pumping system so that it does not pump more fluid than enters the wellbore. Knowing the pump fillage also allows the total amount of fluid produced by the well to be calculated.
Other methods have previously relied on the shape of the graphical representation of the downhole card to compute the pump fillage. For example, U.S. Pat. No. 5,252,031 to Gibbs, entitled “Monitoring and Pump-Off Control with Downhole Pump Cards,” teaches a method for monitoring a rod pumped well to detect various pump problems by utilizing measurements made at the surface to generate a downhole pump card. The graphically represented downhole pump card may then be used to detect the various pump problems and control the pumping unit. Owing to the diversity of card shapes, however, it can be difficult to make a diagnosis of downhole conditions solely on the basis of the shape of the graphical representation. Furthermore, in some instances, such graphical techniques may lead to inaccurate determinations of the pump fillage such that fluid production calculated therefrom may be incorrect.
Accordingly, techniques and systems that rely less on human interpretation in determining the pump fillage would be desirable.